1. Field of the Invention
The present invention relates to a motor-driven steering apparatus applying an assist torque obtained by an electric motor to a steering torque from a steering wheel.
2. Description of the Related Art
Conventionally, as a motor-driven steering apparatus applying an assist torque obtained by an electric motor to a steering torque from a steering wheel, there has been known a structure provided with a steering member reciprocating in a longitudinal direction in correspondence to a rotation of a steering wheel, a ball nut outside inserted to a ball thread shaft formed in the steering member via a plurality of balls, a drive pulley provided in a drive shaft of an electric motor, and a driven pulley coupled to the drive pulley via a belt and integrally rotating with the ball nut (for example, Japanese Patent Application Laid-open No. 2003-291830 (refer to patent document 1)). In accordance with this structure, since the belt is interposed in a power transmission path between the electric motor and the steering member, a vibration or the like from the steering member is not transmitted to the electric motor, and it is possible to maintain a rotational accuracy of the electric motor.
In this kind of motor-driven steering apparatus, a toothed pulley is employed for both pulleys comprising the drive pulley and the driven pulley, and the belt wound around both the pulleys is constituted by a toothed belt, thereby preventing a slip between both the pulleys and the belt.
The toothed pulley employed as the drive pulley is structured such that a plurality of tooth portions are formed with a predetermined interval in a peripheral direction, and the tooth portions are engaged with the belt teeth formed in the belt, thereby efficiently transmitting a rotating force of the drive pulley to the belt. Further, since the belt is moved in an axial direction of the drive pulley at a time of a rotation of the drive pulley, a pair of regulating portions regulating the movement of the belt from both sides in a width direction of the belt are integrally formed in the drive pulley so as to protrude in a collar shape in an outer peripheral direction from both sides in the axial direction of the drive pulley.
However, in this kind of toothed pulley, since it is necessary to form the tooth portions between both the regulating portions, the regulating portions form an obstacle at a time of forming the tooth portions, and there is a disadvantage that it is hard to process the tooth portions.
Accordingly, there has been known a toothed pulley structured by attaching a pair of regulating members operating as the regulating portion to both ends of the pulley main body in which the tooth portions are formed (for example, Japanese Patent Application Laid-open No. 2003-343700 (refer to patent document 2)). Accordingly, the regulating portion does not form an obstacle at a time of forming the tooth portions because each of the regulating members is attached after previously forming the tooth portions in the pulley main body. Thus, it is possible to more easily manufacture.
However, in the case that the drive pulley is structured by the pulley main body and the respective regulating members, there is a risk that the pulley main body and each of the regulating members are carelessly detached during the rotation. Accordingly, it is necessary that a coupling means for firmly coupling the pulley main body and each of the regulating members is provided, and there is a disadvantage that the drive pulley becomes larger in size.
Further, in the case that a taper-shaped inclined surface brought into contact with an end edge of the belt at a time when the belt moves in a width direction is formed in each of the regulating members, it is necessary to correctly attach each of the regulating members to the pulley main body in such a direction that the inclined surface is positioned at the pulley main body side. Accordingly, reassembly work or the like is required in the case where each of the regulating members is attached to the pulley main body in an erroneous direction, and there is a disadvantage that assembly work efficiency is significantly lowered.